netdev - Re: Problems obtaining software TX timestamps

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Message-ID: <4C87FE60.7090209@edu.uni-klu.ac.at>
Date:	Wed, 08 Sep 2010 23:21:36 +0200
From:	Ingo Kofler <ikofler@....uni-klu.ac.at>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	netdev@...r.kernel.org
Subject: Re: Problems obtaining software TX timestamps


On 09/08/2010 05:12 PM, Eric Dumazet wrote:
> Le mercredi 08 septembre 2010 à 14:11 +0200, Ingo Kofler a écrit :
>    
>> Dear all,
>>
>> I am trying to obtain software TX timestamps for a each outgoing packet
>> of an UDP socket. For that purpose I set the SO_TIMESTAMPING socket
>> option to SOF_TIMESTAMPING_TX_SOFTWARE | SOF_TIMESTAMPING_SOFTWARE. The
>> setsockopt call succeeds and also a subsequent getsockopt returns the
>> correct flags. However, if a send a single datagram over the socket and
>> try to fetch the packet as well as its timestamp via the socket's
>> MSG_ERRQUEUE I do not get any information. Rather, the select call waits
>> infinitely on the error queue....
>>
>> I hardly found any documentation on this timestamping mechanism except
>> the text file in the kernel source code. All I've figured out is that if
>> I want to have hardware TX timestamps, I'll have to make a further ioctl
>> which requires root permissions to active the hardware timestamping. But
>> this is not what I want... software timestamps are sufficient for me.
>>      
> To my knowledge, no driver calls skb_tx_timestamp()
>
> You'll need to tweak your NIC driver to play with this TX timestamps
>    
Ok, for hardware timestamps it seems logically for me that the driver 
has to support this. But what about the software timestamps - do they 
also require support from the driver? Is there no generic implementation 
in the networking stack?
>
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>    

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